So-called “function” words were of particular interest to the team, like pronouns and adverbs.

“By themselves they don’t have any meaning, but they clarify what’s going on,” Matthias Mehl, a psychologist at the University of Arizona and lead author of the study, told the scientific journal Nature.

He added that function words “are produced more automatically and they betray a bit more about what’s going on with the speaker.”

If someone is stressed, they tend to talk less, but they also use more adverbs like “really,” and “incredibly.” Mehl told Nature these words may act as “emotional intensifiers,” suggesting the speaker is more “aroused,” meaning excited or alert.

Third-person plural pronouns like “they” and “their” were less common in stressed participants, which could be because when people feel threatened they focus less on the outside world.

The team compared the subjects’ language with the gene activity in their white blood cells, which are known to behave differently when people are in difficult, stressful, or uncomfortable situations.

Comparing the incidence of these words to the white blood cell behaviour was much more accurate than simply asking subjects to say whether they felt anxiety or depression, the researchers found.

Mehl said this research could help with identifying people who are at risk of developing stress-related diseases such as heart disease or a stroke.

Rather than relying solely on self-reports of someone’s mental wellbeing, doctors could listen to the way patients express themselves, and help form a diagnosis that way.